Process for concentrating hydrocarbons



May 23, 1939. F.. E. FREY 2,159,434

PROCESS FOR CONCENTRATING HYDROCARBONS Filed June 27, 1936 JNVENTOR. FREDERICK E. FREY ATTORNEYS.

Patented May 1939 PATENT, OFFICE PROCESS FOR CONCENTRATIN G HYDROCARBONS Frederick E. rm. Bartlesvllle, om, alsignor a Phillips Petroleum Company, a corporation of Delaware Application June 2'1, 1938, Serial No. 87,781

14 Claims.

This invention relates to methods for producing concentrates of desired organic compounds from mixtures of gaseous or readily volatilized organic compounds, and it particularly relates to methods for producing concentrates of certain volatile hydrocarbons.

An object of. this invention is to effect a concentration of certain components of a mixture of organiccompounds by taking advantage of specificity with respect to their molecular weight and unsaturated character.

Another object is to produce a' concentrate oi hydrocarbons of higher average molecular weight than the hydrocarbon mixture being treated.

Another object is to produce a concentrate of hydrocarbons of lower average molecular weight than the hydrocarbons being treated.

Another object is to produce a concentrate richer in unsaturated or cyclic compounds than the material being treated.

Further objects will be apparent from the following disclosure.

The objects .of this invention are attained by taking advantageof the diflerent rates at which different organic compounds will penetrate and pass through a film or diaphragm such as a thin sheet of rubber, or the like. 'lhe objects and practice of this invention depend largely upon the solubility of the organic compound in the diaphragm. Diaphragms suitable for use in my invention are essentially non-porous, in the sense that they contain no microscopic pores such as are found in wood and porous ceramic walls.

It is fully appreciated that the separation of gases by diffusion through a porous diifusion partition has been proposed in U. S. Patent 1,496,757 issued to Lewis, et al., dated June 3, 1924 for Process of separating gases." The rates at which different gases diffuse through such a porous medium vary inversely with the square root of their density or molecular weight, and

while such a method as taught in the Lewis patent hydrocarbons in the vapor state pass through substances such as rubber and the like at rates depending on the molecular weight, saturation and molecular structure of the hydrocarbon molecule. While the exact mechanism by which hydrocarbon vapors pass through rubber and its equivalents, is not understood, the solubility of the hydrocarbon in rubber appears to be the mechanism whereby the hydrocarbon vapor passes into one face and out of the other face of a rubber body. It has been discovered that among the lower parafllns and oleflns the rate of passage through a thin rubber wall increases with molecular weight, and the diffusion rate for a given olefin is more rapid than for a paraiiln of about the same boiling point.

While it is not desired to limit this invention by any single theory, it is believed that the mechanlsm of the method is as follows:

The organic compound, such as hydrocarbon, dissolves in the rubber on the side at which the higher partial pressure of its vapor exists, the dissolved molecules diffuse through the rubber by non-capillary dlflusion and pass to the 0pposite side, and pass from solution into the vapor phase where the lower partial pressure of its vapor exists. For given compounds, the rate of passage through the rubber or other membrane will depend primarily on the solubility o! the compound in the rubber membrane and the rate .of diffusion of dissolved molecules through the membrane. The function will continue as long as a difference of partial pressure of the compound exists between the gas mixtures on the two sides of the membrane. The method is favored and accelerated by removing the gas leaving the membrane by pumping of! or sweeping away by a stream of air or other gas substantially insoluble in rubber. Increasing the total pressure on the diffusing 'gas mixture will increase the overall rate oi diffusion of gas through the'membrane but may decrease the selectivity. In this invention an absolute pressure differential between the two sides does not result in mass motion as it does in the case of diflusion through a porous partition.

It has long been known that hydrocarbons in the vapor state will pass through rubber. I have discovered that among the lower parafllns and oleflns the rate of diffusion through a thin rubber Propane 1.0 Propylene I 1.5 Butane 9.0 Butene-2 22.0

m Isobutylene 7.0 Isobutane 2.0

This difference in diffusion rate is probably due to the diflerence in solubility of the hydrocarbons in the rubber rather than through simple dif- 20 fusion through pores.

Practical embodiments are suggested as follows:-

A rubber membrane is stretched on a supporting wall which must be of perforated conas structi'on or the equivalent. The gas to be diffused is passed under turbulent flow in contact with the rubber. The diffusate passes out from that face of the rubber in contact with the supporting wall and on this side, the exit side, a

so provision for turbulence adjacent to the rubber face -is not necessary, The diffusate is delivered under its own pressure, such as atmospheric pressure,'from the exit face of the rubber, if a pressure suiliciently high is maintained on the other 35 side. togive a partial pressure of diifusate at least as: great as the pressure-to be delivered. This type of construction permits large pressure differences to be maintained without danger of rupturing the rubber. Alternatively, a support 40 for the membrane of less mechanical strength may be used if a diluent gas of relatively insoluble character with respect to rubber be passed along the exit 'face of the diffusion septum. To effect a high degree of concentration a plurality of 45 consecutive stages may be used, the diffusate from one stage serving as the raw material for thenext stage and so on. The gas or vapors leaving any stage except the last may be returned to the inlet vapors entering a preceding stage of similar 50 content of desired diffusate and in this way a 55 intermediate fractions to earlier diffusion stages in the sequence. Obviously, telescoped cylindrical tubes concentrically arranged or an echelon of flat disc-like difiusion septa or other forms may be used to obtain substantially equivalent effect.

60 It is usually best to pass the gases or vapors continuously over the diffusion membrane and in a state of active turbulence. Elevated temperatures, sumciently high to maintain the gaseous state, may be used to permit the treatment of mixtures having a dew point higher than room temperature.

With reference now to the attached drawing, it will be appreciated in what manner one embodiment of the present invention is practiced.

70 Figure 1 diagrammatically illustrates one form of apparatus for practicing the present invention, and,

Figure 2 diagrammatically illustrates an apparatus for practicing a modified form of the 15 invention.

A charge of the hydrocarbon gas to be difi'used is drawn through conduit ID by the pump H and forced into conduit l2 and thereby introduced into a diffusion chamber l3.

There may be a. plurality of diffusion chambers 45 such as the one I3, and in this present description there are illustrated the additional diffusion chambers l4 and I5 which are arranged in series.

The several diffusion chambers l3, l4 and ii are each internally divided into portions or zones A and B by longitudinally disposed division members, or septa, l6, l1 and I8, respectively, which are in the form of thin, rubber membranes, and which are stretched and supported upon suitable members such as the wire supports l9, 20,-and 2|.

The hydrocarbon mixture of gas from which the concentrate or desired hydrocarbons are to, be removed is initially introduced into the zone A of the diffusion chamber l3 and therein, under pressure of the pump ii, and of pump 26 as will presently be explained, it comes in contact with the rubber membrane l6, and a. part of the hydrocarbon mixture or gas charge, is diffused through the membrane into the zone B, or exit side, of the chamber I3.

That part of the'original gas charge, or the part not capable of penetrating the membrane 16 will leave the chamber l3 and the zone A thereof through the discharge conduit 22;

From the exit side of chamber l3, or the zone B thereof, the difl'usate is drawn through a conduit 28 by the pump 24 and forced under pressure into the inlet side, or zone A, of the chamber l4 wherein the pressure upon the gas will force a portion of it through the membrane I! and into the outlet side, or: zone Bsof the chamber.

In portion A of the chamber It all gas not penetrating the membrane I1 is withdrawn through the conduit 25 and forced by the pump 28 into the conduit l2 to be recharged into the zone A, 0 or inlet side, of the first chamber I3. I

Thus it will be appreciated that the diflusate from the first stage of the process, or from the zone B of the chamber ll serves as the charging gas, or raw stoclr, for the second stage of the 5 process effected in chamber H. In this manner the mixture of hydrocarbon gas constituting the charge which is fed to zone A of chamber 43 is under pressure by virtue of'the function of pumps II and 26, and a greater pressure therefore exists 0 in zone A than in-zone B of the chamber l3 because of pump 24 which withdraws the diifusate from zone B by way of conduit 23. By this manner of maintaining a higher pressure in zone A than in zone 'B of the'chamber l3,,and in the zones A and B of all subsequent diflusion chambers to be described, namely, chambers l4 and IS, the concentrates of".desired hydrocarbons are readily collected from the mixture of hydrocarbon gases as'the concentrates are positively forced, go

and/or drawn through membranes.

From the outlet side of chamber II or the zone B thereof, the diffusate-is withdrawn through the conduit 21 by the pump 28 and forced under pressure into the inlet side, or zone A, of chamber I5 wherein the gas contacts the membrane l8 and a portion thereof passes therethrough into the zone B, from whence it is withdrawn through conduit 29 as the product Pump 30 may be interposed in conduit 29 to facilitate the withdrawal of the product from the zone B,'and assist in maintaining it at a lower pressure than zone A. All gas in zone A of chamber l5 which does not I penetrate the membrane I8 is withdrawn therefrom by the pump 3| through the conduit 32 and. is.

-brane 52 and which therefore does not pass.

,much as they maintain a higher pressure in zone A than in zone B of the severaldiflusion chambers and thereby speed the diflusion of the concentrate of the-desired hydrocarbons through the membranes, the invention could be practiced equally as effective if pumps were utilized only to maintain high pressures in zones A of the several diifusion chambers, or if pumps were employed only to maintain reduced pressures in the zones B of the several diffusion chambers.

With reference now to Figure 2 of the drawing I l a modifie form of the presentinvention will be described. The hydrocarbon mixture enters a diffusion chamber 50 by way of conduit 6i and therein contacts in zone A the rubber membrane or septum 52 mounted upon the support 53, and the concentrate of desired hydrocarbons which are soluble in the rubber membrane pass therethrough into zone B. The passage of the concentrate of desired hydrocarbons-from zone A to zone B is assisted by the pump 54 interposed in conduit 55, the full function of which will be presently described.

In zone-A of the diffusion chamber 80 all of the hydrocarbon mixture not soluble in the memthrough it, is exhausted by way of conduit '88. From zone B of the diffusion chamber 50 the concentrate of desired hydrocarbons which diffuse. through the membrane 52 are withdrawn by pump 54 through the conduit 55, and to assist is introduced into zone B of the chamber 50- by way of the conduit 51 and as it flows through zone B it will sweep away from the wall 523 of the membrane 52, the concentrate of desired bydrocarbons and together therewith will be with-- drawn from zone B by virtue of pump 64 through the-conduit 55 and introduced into any type of suitable separator 58 such as an oil scrubber, or

, low temperature condenser, wherein the carrier a single unit or step of the present method, it too is contemplated to be used under desirable circumstances in a series of steps as taught in connection with the description of the apparatus for practicing the invention disclosed in Figure 1; in which case there would be a plurality .of diffusion chambers similar to the one marked 50, which would be arranged in series and each provided with a suitable separator, and the hydrocarbons in zone A of the difluslon chambers which did not difluse through the membrane would be returned to zone A of the preceding diffusion chamber as taught in connection with the description of Figure 1.

The relative rates of passage of pure hydrocarbons through a thin sheet ofrubber separating two gas chambers were found to be as shown in Table I. The rubber sheet was supported against a fine mesh wire screen. In one series of experiments, the absolute pressure of the hydrocarbon was 75 cm. of mercury and in another series it was 115 cm. The gas diffusing through the rubber was removed by. means of a vacuum pump which maintained an absolute pressure of 8-10 mm. of mercury on exit side of the rubber sheet.

' Tam I Relative dlfluston rates of pure hydrocarbons throuah rubber (Propane-1) At pressure At pressure 0176 am. 01115 cm.

mercury mercury An application of the present invention to the concentration of olefin hydrocarbons, particularly the normal olefins, is illustrated by the following example. Mixtures of four carbon atom hydrocarbons obtained by fractionating cracking stillvapors were placed in contact with the rubber sheet as described in the foregoing experiments.

The diffusate was pumped ofl, collected and analyzed with the following results:

Tan: 11

.. Concentration of. ole'fins bu diflusion through rubber Composition of dil Composition msate per cent by of original volume mixture porcent by volume 76 cm. 115 cm.

mercury mercury Isobutcne 23. 20. 9 22. 9 I 35. 47. 4 43. 4 41. 5 31. 8 33. 7

Isobutsne i. 2 2. o l. 2 Normal butanes 18.6 27. 5 20 8 Butanes 80.3 70.5 72.0

These data show a very marked increase in the concentration of the normal butene. They also indicate that the selectivity is lowered somewhat by increasing the total pressure of the gas on the high pressure side of the membrane in order to increase the rate of diffusion. It is obvious from these data that concentrates containing much higher percentages of normal butanes can be obtained by the use of several similar diffusion stages applied consecutively.

Differences in the ingredients compounded with the rubber or in the completeness of curing will affect the specificity for the various hydrocarbons but the most favorable material can be selected by means of simple diffusion tests. Materials other than rubber exerting at least a little solvent action on hydrocarbons may likewise be mechanically supported and used for thepurpose, such as chloroprene rubber, styrene polymer, lacquer films and the like.

By this invention there may be produced from a rough fraction of butanes and butylenes chtained by fractional distillation of cracking still vapors, a concentrate containing a predominance of the 2"-butenes.' I can also effect a concentration of high molecular weight paraifin or olefin hydrocarbons from a mixture containing a. number of homologues. The simpler alicyclic and aromatic hydrocarbons diiluse readily as do the olefins, and a concentrate high in aromaticity or octane number can be obtained by this method.

In some cases liquid hydrocarbons such as gasoline can be separated into fractions diflering in characteristics by this means. Other gases, notably hydrogen sulfide and carbon dioxide, can be removed from a gas stream and concentrated.

I claim:

1. The method of separating from a hydrocarbon mixture a fraction having a higher concentration oi cyclic hydrocarbons, which comprises passing a stream of the said hydrocarbon mixture past'one side of a rubber septum while maintaining a state of reduced pressure on. the other side of said septum to draw the difi'usate from said septum and remove the said concentrate of cyclic hydrocarbons therefrom.

2. The method of separating from a hydrocarbon'mix'ture a fraction having a higher concentration of aromatic hydrocarbons, which comprises passing a stream of the said hydrocarbon.

mixture in contact with one side of a rubber septum while maintaining a lower partial-pressure .on the other side of said septum to draw a diffusate from said septum and to remove the same in the form of a concentration of aromatic hydrocarbons.

3. The method of separating from a hydrocarbon mixture a concentrate of desired hydrocarbons, comprising passing a turbulent stream of the hydrocarbon mixture in a gaseous state in contact with one side of a non-porous diaphragm of a material in which the desired hydrocarbons are more soluble than the other constituents of the mixture, whereby the said desired hydrocarbons dissolve in and diffuse through said diaphragm, and collecting the diflusate at the other side of the diaphragm by pumping oi! the escaping gases thereby maintaining a low partial pressure of the difiusate at the exit side of the said diaphragm.

4. The method of separating from a hydrocarbon mixture a concentrate of desired hydrocarbons, comprising passing a stream 01' the hydrocarbon mixture in contact with'one side of a non-porous diaphragm of a material in which the desired hydrocarbons have a greater solubility than the otherconstitu'ents of the mixture, whereby the said desired hydrocarbons dissolve in and diffuse through said diaphragm, passing a stream of gas relatively insoluble in the diaphragm in contact with the other side of the diaphragm to sweep away and maintain a decreased partial pressure of the difiusate, and recovering the difiusate from the gas.

5. The method of separating from a hydrocarbon mixture a concentrate of desired hydrocarbons, which comprises passing a stream of said hydrocarbons to a zone of elevated pressure, contacting said stream of hydrocarbons in said zone with one side of a non-porous membrane while maintaining a zone of reduced pressure on the other side of said membrane, causing desired hydrocarbons to dissolve in and difiuse through said membrane and to pass from said zone of elevated pressure to said zone of reduced pressure, withdrawing the difiusate from said zone of reduced pressure and passing it to a second zone or elevated pressure, contacting said diffusate in said second zone of elevated pressure with one side or a second non-porous membrane while maintaining a second zone of reduced pressure on the other side of said membrane, causing de-' sired hydrocarbons to dissolve in and difiuse through said second membrane and to pass from said second zone of elevated pressure to said second zone oi! reduced pressure, withdrawingfrom said zone of reduced pressure a concentrate of said desired hydrocarbons, and withdrawing from said second zone 01' elevated pressure hydrocarbons not diflused through said second membrane and returning said hydrocarbons to said first mentioned zone of elevated pressure.

8. The method of preparing a concentrate of desired hydrocarbons from a complex gaseous hydrocarbon mixture, which comprises subjecting the said mixture to consecutive selective diffusion stages, each stage being accomplished in a chamber consisting of two portions separated by a supported non-porous membrane of .a ma.-

' terial in which the desired hydrocarbons are more soluble than other constituents of the mixture, wherebythe said desired hydrocarbons dissolve in and difluse through said membrane, elevating the pressure of the difiusate from one stage and passing it into the next stage, returning the undiflused residue gas leaving each stage, except the first, to the inlet gases entering a preceding stage of similar content of desired hydrocarbons, and collecting the diffusate from the final stage.

7. The method of preparing a butene-2 concentrate from a butene-butane mixture such as the tour carbon atom, traction of cracking still gases, which comprises subjecting the said butenebutane mixture to repeated diffusion through nonporous rubber membranes 8. The method of separating from a hydrocarbon mixture a concentrate of desired hydrocarbons, which comprises passing a liquid hydrocarbon mixture in contact with one side of a non-porous diaphragm of a material in which the desired hydrocarbons are more soluble than the other constituents of the said mixture, whereby the said desired hydrocarbons dissolve in and diffuse through said diaphragm, and collecting the diflusate at the other side of the said diaphragm in a zone maintained at a-reducedpressure.

9. The method of separating from a hydrocarbon mixture a concentrate of desired hydrocarbons, which comprises passing a liquid hydrocarbon mixture in contact with one side of a non-porous diaphragm of a material inv which the desired hydrocarbons are more soluble than the other constituents of the said mixture, and

passing a stream of gas in contact with the other side of said diaphragm to withdraw therefrom and to collect a concentrate of the desired hydrocarbons dissolving in and diffusing through said diaphragm.

10. The method of producing concentrates of olefin hydrocarbons from gaseous mixtures containing olefin and paraflin hydrocarbons which comprises passing a gaseous mixture containing olefin and parafiin hydrocarbons in turbulent flow past one side oi a rubber septum and removing the gases which pass from the opposite side of said rubber septum.

11. A process for. separating hydrocarbons of higher molecular weight from hydrocarbons of lower molecular weight which comprises passing a gaseous mixture containing two or more hydrocarbons of different molecular weight in turbulent flow past one side of a rubber membrane and removing the gases containing hydrocarbons of higher molecular weight from the opposite side of said membrane.

12. The 'method oi producing concentrates of unsaturated hydrocarbons from gaseous mixtures which comprises passing a gaseous mixture containing unsaturated hydrocarbons under a pressure in turbulent flow past one side of a rubber septum, maintaining the other side of said rubber septum under a lower pressure and recovering the unsaturated hydrocarbons which pass from the other side of said rubber septum.

13.'A method of separating isomeric oleilns Y 'from hydrocarbon mixtures which comprises passing a hydrocarbon mixture containing at least two oleflns of the same molecular weight flow past one side of a rubber membrane, and

removing gases containing one of said oleflns in a more concentrated state from the opposite side of said membrane.

14. A method of separating isobutene from butene-2 which comprises passing a hydrocarbon mixture containing butene-2 and isobutene past one side of a rubber membrane, whereby butene-2 dissolves in and passes through said rubber membrane more readily than isobutene, and removing gases containing butene-2 in a more concentrated state from the opposite side of said membrane.

FREDERICK E. 

